No clue about the specific's for a Deb based Apache setup (why they had to dork the standard httpd setup I'll never understand).
But....when ever you run into a brick wall, go back to square one and start over.
Your IP number takes you to the Apache welcome page, so Apache in general is working.
Since your domain URL is fubar'd, start there.
Reset your httpd/vhost config file (whatever it's called in Ubuntu) and make a VERY SIMPLE Config (no rewrites, no redirects, no symbolic links, no aliases), just the very BASIC domain setup.
When you get that working (i.e. you can browse to
www.yourdomain.com) then make a backup copy of that config file.
Then add one (and only one) new addition to the config file. Does it work? Yes, make a new backup copy. No, restore the last working copy and try again.
And remember - every time you change the config file(s) you need to restart Apache.